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The photographic news
- Bandzählung
- 35.1891
- Erscheinungsdatum
- 1891
- Sprache
- Englisch
- Signatur
- F 135
- Vorlage
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- Hochschule für Grafik und Buchkunst Leipzig
- Digitalisat
- SLUB Dresden
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- Public Domain Mark 1.0
- URN
- urn:nbn:de:bsz:14-db-id1780948042-189100009
- PURL
- http://digital.slub-dresden.de/id1780948042-18910000
- OAI-Identifier
- oai:de:slub-dresden:db:id-1780948042-18910000
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- Fotografie
- LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1715, July 17, 1891
- Digitalisat
- SLUB Dresden
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- Ausgabe
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- Wahlperiode
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Zeitschrift
The photographic news
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Band 35.1891
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Band 35.1891
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50G THE PHOTOGRAPHIC NEWS. [July 17, 1891. many windows. These windows were naturally re flected by the surface of the bubble, in the way familiar to anyone who has ever blown a bubble within doors. Now a certain English artist had painted a picture of a garden with some children playing in the foreground, and in order to give a little variety to the group he made one of the little ones to blow soap-bubbles. Unfortunately, however, instead of painting from an actual bubble, he copied the coloured photograph in the book referred to, the bubble with windows; but as gardens generally have no windows, the thing was a little out of place. We are next told of a picture exhibited last year in which the dark half of the moon was turned towards the sun, and of a still stranger case in which, from the assumed position of the sun, the moon, to be correct, ought to have been painted full, but the artist had ex pressed it as a crescent. He owned that he knew it was wrong, and, in fact, had painted it full originally, but had altered it because “it destroyed the balance of his picture.” “That, you see, is where the art comes in,” added the lecturer at the close of his anecdote. In another case—the picture is hung in the present Academy exhibition—a painter has fallen foul of the well-known phenomenon of refraction, and has made the apparent bend in a body immersed in water to bend the wrong way. A rainbow seen as an arch viewed in perspective is, from its nature, a simple impossibility, and yet many artists have depicted a rainbow so, possibly because if it were otherwise rendered it might, as the mooney gentleman said, “destroy the balance of the picture.” Many other faults common to artists were pointed out and expatiated upon in this excellent paper, but the greater number refer to mistakes due to a wrong appre ciation of the laws which govern colour in nature. In this domain the artist has it all his own way, and photography can be of no service to him ; but where mere form is concerned, he will find that the camera can teach him many things, and may possibly be the means of preventing him falling into error. NEW ZINCOGRAPHIC PROCESS. BY AUGUST AND LOUIS LUMIERE. The method which we propose may be described as a modification of the albumen process. The facility and the rapidity with which it allows you to produce engraved images of the greatest delicacy and fineness, and the employment as a lined screen of a positive phototype, constitute incontestable advantages. The greater part of the mechanical processes in use require the employment of a reversed negative, which must be both transparent in the shadows and opaque in the lights—conditions some what difficult to secure—while the manipulations are of a delicate nature, and can only be carried out satisfactorily by experienced hands. Our new method does not possess these difficulties of procedure, and, by following exactly the directions which follow, it is possible to obtain at the first attempt images perfect in their nature, and susceptible of furnishing excellent lithographic prints, or blocks ready for the typographic press. The following solution is first of all prepared:— Water ... ... ... ... ... 1,000 parts Albumen (from fresh eggs) ... ... 100 „ Bichromate of ammonia ... ... 3 ,, (The amount of bichromate should be sufficient to colour the solution a light yellow.) This mixture is rapidly stirred, carefully filtered, and, by means of a whirling table, is spread upon a sheet of polished zinc, which has been previously carefully cleaned. As soon as the thin coating of bichromated albumen has been deposited on the zinc in this way, it is necessary to hasten the drying of the com pound by lightly heating the metal plate. The plate is then exposed to the light in a printing frame under a positive, and, when the exposure is judged to be sufficient, it is removed from the frame, and is given a coating of ink, thinned with middle varnish, by means of a roller. The colour of the surface should then be a dark grey, not black, and without any appearance of the image. The plate is now immersed in tepid water, and before long the image begins to appear, and the action may be helped by lightly rubbing the surface of the zinc with a tuft of cotton-wool. The image is a negative one, and the shadows of the picture consequently are represented by patches of bare zinc, the albumen on these parts having been protected during the exposure to light, and therefore remaining soluble. It is these portions that have been washed off in the bath of tepid water. The plate is now thoroughly washed in plenty of water, and plunged into a solution of perchloride of iron at 359 B., in which it should remain from ten to fifteen seconds. It is now again washed and dried. The zinc plate is next heated to about 50°, and a roller charged with black ink thinned with middle varnish is passed over it, when it will be found that the ink will adhere to the whole of the surface indiscriminately. By means of another roller, passed several times over the surface of the plate, it is possible to remove the ink from those portions still covered with the insoluble albumen. There only remains now to rub the plate with a soft rag charged with strong ammonia, when the image appears in black on a brilliant background of metallic zinc, for the albumen, although insoluble by light, is soluble in ammonia, and a second development is thus brought about which is the reverse of the first. By the friction, as well as by the action of the ammonia, the ink and albumen are removed, while the ink remains on those portions of the plate whicli have been partially engraved by the action of the perchloride of iron. It is the latter reaction which forms the basis of our method, and which constitutes its novelty. It is very curious to watch this reversal of the image under the influence of the ammonia. Solutions of potash, soda, &c., do not give such clean results, probably because of the saponification which is induced by the presence of the fatty constituents of the ink. If the plate has to be printed from lithographically, there only remains to prepare it in the usual manner. If, on the contrary, we require the image to be in relief, it is necessary to sprinkle over the surface powdered resin, and warm it in the usual way before proceeding to the first etching, or biting-in with acid. In this latter case it is preferable to shorten the immersion of the plate in the perchloride of iron solution, in order to avoid roughening too much the surfaces which are ultimately destined to stand up in relief.
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